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Topic: safe to use an RS232 "Y" splitter to connect one comport to two recipients? (Read 986 times) previous topic - next topic

kp3ft

Hi all,
I'm hoping someone can help us out with a particular problem:

We have a piece of equipment that can send logging data through a parallel port to a printer, or ASCII data through a serial port to a computer, but not both at the same time.  The computer runs HyperTerminal for capturing the ASCII to a text file.  The printer is an old dot-matrix for printing the log.
We want to be able to log to the printer and computer at the same time, so that the computer would be a redundant backup in case the printer jams or fails .  The tested and working DB9 serial port connection to the computer is just three pins:
Pin2 - RXD
Pin3 - TXD
Pin5 - Ground
9600 baud, no parity, 8-bit, 1 stop-bit, no flow control
(Not sure if I even need the the RXD connected on the equipment-side, because it is only sending data, but haven't tested that yet.)

I was thinking to split the serial-out of the equipment with a simple "Y" adapter, so that one branch goes directly to the computer and the other branch goes to a serial-to-parallel converter for the printer.  Would this work, or will I fry something?  Maybe another option would be to split the parallel-out of the equipment so one branch goes directly to the printer and the other branch goes to a parallel-to-serial adapter.
Thanks for any help

CrossRoads

Yes, One source can transmit to two receivers.
I used to split out both Rx & Tx lines and watch them on a PC, monitor the traffic going both ways.
Made for a handy protocol analyzer.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

kg4wsv

Quote
was thinking to split the serial-out of the equipment with a simple "Y" adapter, so that one branch goes directly to the computer and the other branch goes to a serial-to-parallel converter for the printer.  Would this work, or will I fry something?


The RS232 spec calls for one TX connected to one RX.  So multiple receivers don't meet spec.

In practice, it'll probably work, but maybe not at high speeds.

I doubt anything will fry, as long as no more than one TX is driving.

-j

Grumpy_Mike

Quote
as long as no more than one TX is driving.

Ah there's the rub. If your devices ever send acknowledge messages or Xon / Xoff protocol then you are stuffed.

retrolefty

Yes an output signal can be wired to more then one input signal as long as they are of compatible voltage logic levels. Another problem is to be sure which side of the comm link you want to split off. If the equipment is designed to normally 'talk' to a PC on a standard DE-9 comm port connector then you equipment is transmitting it's information on the PC's rec pin, if that makes sense.

Lefty

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